Seecar

I just fire off my 98 LS1 Motor after a rebuild (rod bearing, main bearing, hot cam install, 80 MM TB and 85 MM MAF etc..)and I'm hearing a blow back sound through the air cleaner. The sound is not constant but pulsing. Other than that the engine sounds good and has good oil pressure but can understand what is causing this sound. Any help would be appreciated.

Thanks

elias_799

iTrader: (8)

can you make a video of the sound so we can more clearly diagnose your problem ?

Seecar

I will try and capture the sound and post it. It sound a like when you exhale pause then exhale over and over.

Thanks

faster_n_you98

iTrader: (31)

I have a K&N FIPK II kit and mine makes a pretty loud sucking sound until it warms up. Dunno if that helps or not but i figured id throw it out there.

Seecar

I found out what was causing the sound. I disconnect the IAC motor wiring and the sound when away. Reconnected and the sound cam back. Apparently there must be a pressure build up in the intake and when the ECM tells the IAC to open, the sound is pushing back throught the TB. I have long tubeing from the aftermarket filter to the input of the TB. Plenty of length to echo the sound. I've read that GM reduced that sound by using a short run between the Air Filter and TB. Glad to know it wasn't anything drastic.....



Thanks to all that replied!

12secSS

iTrader: (30)

Has it been tuned? If not, it just means you need to have the idle settings tuned. The IAC valve is moving through a large range to keep the engine from stalling. The noise you here is the IAC valve fully opening, then it almost/fully closes and the noise goes away. Get it tuned!

Seecar

No the motor has not been tuned. I do plan to have the fine tuning done by a professional tuner once the vehicles returns from the interior shop....Thanks for your input.